JPH07116605B2 - Hydrogenated amorphous germanium film, method for producing the film, and electronic device or electronic apparatus using the film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a hydrogenated amorphous germanium film, a method for manufacturing the film, a photovoltaic device using the film, an optical sensor, an electrostatic latent image carrier, The present invention relates to an electronic device or an electronic device such as a laser printer.

(B) Conventional technology Amorphous silicon (hereinafter referred to as a-Si) as a photoactive layer or a photoconductive layer of a photovoltaic device, a photosensor, an electrostatic latent image carrier, or the like.
Semiconductors are often used. High-efficiency photovoltaic devices currently used for solar power generation, applications as infrared sensors in photosensors, and LED printers as lasers for electrostatic latent images, laser printers, etc. In order to have sensitivity, research on making the optical bandgap of a-Si into a narrow band gap has been actively pursued. Germanium (Ge) is a substance considered to be the most effective in achieving a narrow band gap in such a semiconductor material.

By adding Ge to a-Si, the optical bandgap of the semiconductor material is about 1.
Although it can be set to any value from 7eV to 0.9eV, Japan Jo
ural of Applied Physics Vol.25 No.1 (1986) L54-L56, it is known that the network density decreases with increasing Ge addition amount, and the film quality decreases. There is.

As a measure for improving such a network, it has been proposed to use a film forming method such as a hydrogen dilution method or a triode method. However, although this method is effective for a film having an optical bandgap of 1.4 eV or more, it improves the network for a film having a large Ge addition amount, in other words, a film having a narrow optical bandgap. Has not reached. In particular, since amorphous germanium (hereinafter abbreviated as a-Ge) does not contain Si, the optical bandgap is narrower at 0.9 to 1.0 eV as compared with the above amorphous silicon germanium, and the photosensitivity characteristic in a long wavelength band is improved. However, the fact that the density of the film is still low has not been improved, so that the defect density is high. Therefore, in a photovoltaic device, an optical sensor, an electrostatic latent image carrier, or other electronic device for which a narrow bandgap material having an optical band gap is required, or in an electronic device incorporating such an electronic device, a long wavelength is used. Satisfactory results have not been obtained in the band photosensitivity characteristics.

(C) Problem to be Solved by the Invention Although a-Ge is promising as a narrow bandgap material having an optical bandgap as described above, the present invention can obtain only a low-density film and has a low density. Since only dense films can be obtained, there are many defect densities, and in electronic devices and electronic devices that use the narrow bandgap material, satisfactory results cannot be obtained in the photosensitivity characteristics in the long wavelength band. It is what

(D) Means for Solving the Problems In order to solve the above problems, the present invention uses a hydrogenated a-Ge film as a narrow band gap material, and
The a-Ge film is characterized by having a refractive index of about 4.0 or more in a wavelength band of 1500 to 2500 nm. Further, such a hydrogenated a-Ge film is obtained by setting the temperature of the substrate surface to about 225 to 275 ° C. and decomposing the source gas containing at least GeH ₄ gas introduced into the reaction vessel. Furthermore, in a stacked photovoltaic device in which a plurality of unit power generation elements are stacked in the light incident direction, a refractive index in the wavelength band of 1500 to 2500 nm is about 4.0.
The unit power generating element having the hydrogenated a-Ge film as a photoactive layer is provided on the back side as viewed from the light incident side, and the photoactive layer of the unit power generating element disposed on the light receiving surface side is the a-Ge film. It is characterized by being wider than the optical band gap of.

The photosensor is characterized in that the photoactive layer is a hydrogenated a-Ge film having a refractive index of about 4.0 or more in the wavelength band of 1500 to 2500 nm. Further, the electrostatic latent image carrier is characterized in that a hydrogenated a-Ge film having a refractive index of about 4.0 or more in a wavelength band of 1500 to 2500 nm is used as a photoconductive layer and is disposed on the conductive surface of the substrate. Such an electrostatic latent image carrier, charging means for charging the carrier with electric charge, an infrared laser optical head for writing the electrostatic latent image on the carrier, and developing the electrostatic latent image into a visible image. Developing means for

(E) Action As described above, the hydrogenated a-Ge film has a refractive index of about 4.0 or more in the wavelength band of 1500 to 2500 nm, so that the density of the network can be increased. By further increasing the density, a narrow bandgap material having a reduced defect density and improved film quality can be obtained. Further, the temperature of the substrate surface is set to about 225 to 275 ° C., and at least it is introduced into the reaction vessel.
By decomposing the source gas containing GeH ₄ gas, the reaction of substrate surface reaction at low temperature and the transition to thermal decomposition at high temperature are suppressed.

(F) Example A hydrogenated a-Ge film was formed by using a well-known plasma CVD method. Table 1 below shows film forming conditions by the plasma CVD method.

Figure 1 shows the hydrogenated a-G obtained by the plasma CVD method.
This shows the dependency of the deposition rate of the e-film on the substrate temperature. Under such film forming conditions, the hydrogenated a-Si film obtained by the plasma CVD method using SiH ₄ gas instead of GeH ₄ gas has the temperature dependence of the hydrogenated a-Ge film shown in FIG. It does not show such remarkable dependence. This suggests that the hydrogenated a-Ge film has a unique reaction mode different from that of the hydrogenated a-Si film. FIG. 2 shows how the specific temperature dependence of the film formation rate has an influence on the formed hydrogenated a-Ge film with respect to the refractive index. As a result of the measurement of the refractive index, it was found that the refractive index has a close relationship with the film forming rate shown in FIG. That is,
The higher the film formation rate, the smaller the refractive index and the lower the density of the film network.

As a result, the film deposition rate is about 2 ° C, which is the slowest, around
It can be seen that the refractive index as high as about 4.0 or more in the wavelength band of 1500 to 2500 nm can be obtained in the temperature range of 25 to 275 ° C. That is, the refractive index of the conventional a-Ge film is 1986.
MITI / NEDO-EPRI Jo held in Osaka from November 11 to 14, 2014
It was about 3.8 that was announced at the int Workshop, and by setting the substrate surface temperature to about 225 to 275 ° C, a high density hydrogenated a-Ge film with a significantly improved refractive index can be obtained. . The reason for this is that when the substrate temperature is low, only a sparse film is formed due to insufficient reaction on the substrate surface, and when the substrate temperature is high, the decomposition form of the source gas shifts to thermal decomposition as well as plasma decomposition. It is considered that the film speed increased to become a sparse film, or even if the film was a dense film, hydrogen was released and eventually became a sparse film. Therefore, a high refractive index a that brings about a high density of the network
It can be seen that the temperature of the substrate surface is a very important factor for obtaining the -Ge film.

Figure 3 shows the PDS (Photothermal Defl) of such hydrogenated a-Ge film.
ection Spectroscopy) Shows the result of spectrum measurement.
The hydrogenated a-Ge film formed at 250 ° C, which can obtain a high refractive index, shows a sharp decrease in absorption coefficient. Therefore, the hydrogenated a-Ge film formed at other temperatures has a lower refractive index. It shows that the defect density in the energy band gap is low. That is, increasing the density of the network effectively acts to reduce the defect density, and provides an a-Ge film that is a high quality narrow band gap material.

FIG. 4 shows a stacked photovoltaic device as an application example to an electronic device using such a high quality a-Ge film. In this embodiment, the first to fourth unit power generating elements (SC ₁ ) to (SC ₄ ) provided with a semiconductor junction such as a pin junction parallel to the film surface so as to be capable of photoelectric conversion operation by themselves are made of glass or the like. It is placed on the light-receiving surface electrode (2) made of ITO and SnO _{2 on the} optical substrate (1), and the metal back electrode (3) is provided on the back surface at the rear end as seen from the light incident side. It is a stacked photovoltaic device. Each unit power generation element (SC ₁ ) to (SC ₄ ) has a pin as described above.
I-type layers (i ₁ ) to (i ₄ ) that have a junction and are mainly used for light having a wavelength shorter than the wavelength based on the optical band gap when light is incident.
At this point, the photo-carriers of electrons and / or holes, which perform absorption operation and contribute to power generation, are generated. Therefore, the first and second i-type layers (i ₁ ) that operate as photoactive layers in the first and second unit power generating elements (SC ₁ ) and (SC ₂ ) provided on the light incident side,
(I ₂ ) is hydrogenated a-Si with an optical band gap of about 1.6 to 1.7 eV.
It is composed of a film, and is composed of the following 3rd unit power generating element (SC ₃ ) _3rd i-type layer (i
₃ ) is formed from a hydrogenated a-SiGe film having an optical bandgap of about 1.4 eV, and the 4i-th layer (i ₄ ) of the 4th unit power generation element (SC ₄ ) at the end is an optical bandgap. Is about 0.9-1.0 eV and
It is composed of a hydrogenated a-Ge film having a refractive index of about 4.0 or more in the wavelength band of 1500 to 2500 nm. In addition, the first and the first
The refractive index of the hydrogenated a-Si film of the 2i-type layers (i ₁ ) and (i ₂ ) is 3.4.
And the refractive index of the hydrogenated a-SiGe film of the _third i-type layer (i ₃ ) is
3.7, and the optical power of reducing the interface reflection in the i-type layers (i ₁ ) to (i ₄ ) of each of the first to fourth unit power generating elements (SC ₁ ) to (SC ₄ ) as much as the latter element Are satisfied with the demand.

The basic characteristics of the photovoltaic device having the structure of the present example were measured using a solar simulator that artificially irradiates sunlight (AM-1, 100 mW / cm ² ) immediately below the equator. The results are shown in Table 2 below. For comparison, a hydrogenated a-Ge film having a refractive index of about 3.8 was used as the _fourth i-type layer (i ₄ ) of the fourth unit power generation element (SC ₄ ) although the optical bandgap was the same. Other than the above, a comparative example device having the same configuration was prepared, basic characteristics were measured, and the results are also shown in Table 2.

In the stacked photovoltaic device in which a plurality of unit power generation elements are stacked in the light incident direction as described above, an a-Si film or an a-SiGe film having a wide optical bandgap is provided on the light receiving surface side of the photoactive layer (i ₁ ) ~
(I ₃₎ first to third unit power generating device having a (SC ₁₎ ~ (S
C ₃ ), and a hydrogenated a-Ge having a narrow optical band gap and a refractive index of about 4.0 or more on the back side of the _first to third unit power generating elements (SC ₁ ) to (SC ₃ ). By providing a fourth unit power generation element (SC ₄ ) having a film as a photoactive layer (i ₄ ), a hydrogenated a-Ge film having a small refractive index of about 3.8 despite having the same optical band gap. The conversion efficiency was improved by about 16% as compared with the comparative column device including the fourth unit power generation element having the photoactive layer as a light emitting layer.

FIG. 5 shows an embodiment in which the hydrogenated a-Ge film is applied to an optical sensor having a photosensitive peak in the infrared region of wavelength 800 to 900 nm. That is, a pin-junction type semiconductor film (12) is provided on one main surface of a transparent substrate (10) so as to cover a light-receiving surface electrode (11) of a metal comb-type or lattice-type collector electrode structure. A back electrode (13) made of metal is laminated on.
The semiconductor film (12) is a p-type layer (12p) of a hydrogenated a-SiGe film when viewed from the light-receiving surface electrode (11) side, and a refractive index (wavelength of 1500 to 2500 nm that operates as a photoactive layer that generates photocarriers). I-type layer (12i) of hydrogenated a-Ge film with a band value of about 4.0 or more
And a n-type layer (12n) of hydrogenated a-Ge film having a refractive index of about 4.0 or more. Thus, an optical sensor using a hydrogenated a-Ge film having a refractive index of about 4.0 or more in the wavelength band of 1500 to 2500 nm as a photoactive layer is a hydrogenated a-Ge film having a refractive index of about 3.8 as a photoactive layer. It was confirmed that the short-circuit photoelectric current value increased by about 20% in the infrared region of the wavelength band of 800 to 900 nm, compared with the conventional optical sensor.

FIG. 6 shows an application example in which a hydrogenated a-Ge film is used for an electrostatic latent image carrier such as a plain paper copying machine and a laser printer. Normally, the electrostatic latent image carrier has a cylindrical shape. In the figure, a partial cross section is drawn. That is, the hydrogenated a-Ge film having a refractive index of about 4.0 or more in the wavelength band of 1500 to 2500 nm is a conductive surface of the cylindrical substrate (20) (when the substrate itself is made of a conductive material such as aluminum, its surface, A photoconductive layer (21) is formed to cover the substrate itself, which is a conductive thin film if it consists of a composite of insulating material such as glass or heat-resistant plastic and ITO, SnO ₂ , or a conductive thin film such as a metal thin film that covers the surface. To do. Such a photoconductive layer (21) is electrically conductive at a portion irradiated with light, and after uniformly charging the surface thereof,
By selectively irradiating light, the photoconductive layer (21) in the portion that has received the light is electrically connected and the electric charge is discharged. Therefore, the surface of the photoconductive layer (21) is selectively discharged with the electric charge at the portion irradiated with light, and as a result, a positive or negative electrostatic latent image is carried by the remaining electric charge.

Thus, by using the hydrogenated a-Ge film having a refractive index of 4.0 or more as the photoconductive layer (21) of the electrostatic latent image bearing member carrying an electrostatic latent image, the conventional hydrogenated a-Ge film having a refractive index of 3.8 is used. Compared to an electrostatic latent image carrier having an a-Ge film as a photoconductive layer, the charging ability can be increased by about 10%, and the photosensitivity in the wavelength band of 800 to 900 nm can be increased by about 20%. It was

In such an electrostatic latent image carrier, the photoconductive layer (21) was formed directly on the conductive surface of the substrate (20), but if carrier injection from the substrate (20) side occurs, the substrate will be removed. A blocking layer composed of a p-type or n-type doped hydrogenated a-Ge film is inserted between the photoconductive layer (21) and the photoconductive layer (21), or SiN or SiC is formed on the surface of the photoconductive layer (21). A surface layer made of an insulating material such as SiO 2 may be appropriately provided.

FIG. 7 shows a schematic structure of a laser printer incorporating such an electrostatic latent image carrier. Hydrogenated a-Ge with high refractive index
Cylindrical electrostatic latent image carrier (3 with photoconductive layer (21)
(0) is provided with a charging means (31) for uniformly charging positive or negative charges on the surface in the vicinity of the outer peripheral surface thereof, and the electrostatic latent image carrier having the charges held by the charging means (31). By rotating, (30) moves to the irradiation position of the laser beam and the electrostatic latent image writing operation is performed. In writing such an electrostatic latent image, considering that the photoconductive layer (21) is composed of a hydrogenated a-Ge film and the photosensitivity in the infrared region of wavelength 800 to 900 nm is increased by about 20%, It is performed by using an optical head (32) composed of a laser, especially an infrared semiconductor laser. That is, the laser beam emitted from the optical head (32) reaches the photoconductive layer (21) through the lens system (33) and the rotating polygon mirror (34), and the charge at the irradiated site is caused to flow out to the substrate (20) side, so that the residual charge To form an electrostatic latent image. Such an electrostatic latent image is developed into a visible image by the toner charged to the opposite polarity of the developing means (35) with the rotation of the carrier (30), and then the toner follows the conveyance route indicated by the broken line. The plain paper sent from the paper feeding means (36) is transferred as it passes over the transfer means (37), and the fixing means (3
It is fixed by 9). Electrostatic latent image carrier after transfer (30)
The surface of the surface is cleaned by removing the residual toner by the cleaning means (40) and finally discharged by the charge removing means (41) to prepare for the next series of processes including charging, writing, development, transfer and cleaning.

(G) Effect of the Invention The hydrogenated a-Ge film of the present invention is, as is clear from the above description,
Since the density of the network can be increased, a narrow bandgap material having a reduced defect density and improved film quality can be obtained. Further, such a hydrogenated a-Ge film can be easily formed by simply using GeH ₄ gas as a source gas and controlling the substrate temperature within a specific range, so that a complicated manufacturing process is not required. Further, a hydrogenated a-Ge film having an improved film quality is required to have a narrow bandgap, a photoactive layer of a rear-side unit power generation element of a stacked photovoltaic device, a photoactive layer of an infrared photosensor, By using it for the photoconductive layer of the electrostatic latent image carrier, the characteristics of the device itself can be improved, and long-wavelength light characteristics can be improved even in the laser printer incorporating the electrostatic latent image carrier. .

[Brief description of drawings]

1 to 7 are for explaining the present invention, and FIG. 1 is a measurement diagram showing the relationship between the substrate temperature and the film formation rate,
Fig. 2 is a measurement diagram showing the relationship between substrate temperature and refractive index, Fig. 3 is a PDS spectrum characteristic diagram of amorphous germanium hydride formed at various substrate temperatures, and Fig. 4 is an implementation of a stacked photovoltaic device. FIG. 5 is a schematic sectional view showing an example of an optical sensor, FIG. 6 is a schematic sectional view showing an example of an electrostatic latent image carrier, and FIG. 7 is a laser printer. And a conceptual configuration diagram showing the embodiment of FIG. (SC ₁ ) to (SC ₄ ) ... 1st to 4th unit power generating elements, (i ₁ )
~ (I ₄ ) …… first to _fourth i-type layers, (12) …… semiconductor film,
(20) ... Substrate, (21) ... Photoconductive layer, (30) ... Electrostatic latent image carrier, (31) ... Charging means, (32) ... Optical head, (35) ... Development Means, (36) …… Paper feeding means, (37)
...... Transfer means, (39) …… Fixing means, (40) …… Cleaning means, (41) …… Electrifying means.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/205 31/04

Claims (6)

[Claims] 1. A hydrogenated amorphous germanium film having a refractive index of about 4.0 or more in a wavelength band of 1500 to 2500 nm. 2. A method for producing a hydrogenated amorphous germanium film on a substrate surface by introducing a raw material gas containing at least GeH ₄ gas into a reaction vessel and decomposing the raw material gas, wherein the temperature of the substrate surface is controlled. A method for producing a hydrogenated amorphous germanium film, characterized in that the temperature is about 225 to 275 ° C. 3. A stacked photovoltaic device in which a plurality of unitary power generating elements are stacked in the light incident direction, wherein a photoactive layer comprises a hydrogenated amorphous germanium film having a refractive index of about 4.0 or more in a wavelength band of 1500 to 2500 nm. And a photoactive layer of the unit power generating element arranged on the light receiving surface side is wider than the optical bandgap of the amorphous germanium film. Stacked photovoltaic device. 4. An optical sensor comprising a photoactive layer of a hydrogenated amorphous germanium film having a refractive index of about 4.0 or more in a wavelength band of 1500 to 2500 nm. 5. An electrostatic latent image carrier comprising a photoconductive layer of an amorphous germanium hydride film having a refractive index of about 4.0 or more in a wavelength band of 1500 to 2500 nm, which is disposed on a conductive surface of a substrate. 6. An electrostatic latent image carrier according to claim 5, charging means for charging the carrier with an electric charge, an infrared laser optical head for writing an electrostatic latent image on the carrier, and the electrostatic device. A laser printer comprising: a developing unit that develops a latent image into a visible image.